To provide the participants in the "Antigen Recognition by T cells" program project with complete, state-of-the-art, digital imaging microscopy services. This will include live-cell imaging and three- dimensional of fluorescently labeled fixed cells. In live cell imaging the spatial and temporal movement of GFP-tagged proteins will be analyzed as well as the localization and oscillatory behavior of [Ca++} fluxes. The three-dimensional analysis would enable to measure both quantitatively and qualitatively the co distributions of up to four labels simultaneously. Similar analysis will be performed on fixed tissue sections. The core will be used in all projects and is invaluable for the successful completion of the proposed Aims.